Superabsorbent polymer system

Superabsorbents. Water-sweUable polymers are used extensively in consumer articles and for industrial appUcations. Most of these polymers are cross-linked acryUc copolymers of metal salts of acryUc acid and acrylamide or other monomers such as 2-acrylamido-2-methylpropanesulfonic acid. These hydrogel forming systems can have high gel strength as measured by the shear modulus (134). Sometimes inorganic water-insoluble powder is blended with the polymer to increase gel strength (135). Patents describe processes for making cross-linked polyurethane foams which contain superabsorbent polymers (136,137). 

Superabsorbents are superabsorbent polymers, which are loosely crosslinked hydrophilic polymers and have ionic charges in the polymers. They absorb water, swell, and retain aqueous solution above hundred times their own weight. Because of the excellent characteristics, the superabsorbents have been widely used in many applications such as disposable diapers, feminine napkins, soil additives in agricultural or horticultural applications, gel actuators, water-blocking tapes, materials for drug delivery system, absorbent pads, etc., where water absorbency or water retention is important. 

Superabsorbent polymers are used as a liquid-absorber in food packaging systems. In these systems, the superabsorbent polymers absorb juice or water from fresh foods such as raw chicken, shellfish, and other meats or from frozen foods as they thaw. Chilled superabsorbent polymer gels may also be used as a dry-cooling medium. The water-swollen gel, contained in a durable plastic bag, is frozen and used to keep perishable foods cold. In addition to its liquid-water-absorption characteristic, superabsorbent polymers absorb water from the vapor state and therefore may be used to control humidity. 

Sensor The swellability of superabsorbent polymer gels, their mechanical modulus and rubbery character, and their sensitivity to changes in water content, pH, and ionic strength make them suitable for use in various sensing systems. 

The basic component of tiie erqimimental system applied to this study was an absorbent material normally used in personal hygiene articles. In principle tiiis would be loose or bonded cellulose flufi possibly blen with cross-linked sodium polyacrylate granules (known as superabsorbent polymer, SAP) for enhanced liquid capacity. Cellulose fibers or whole composites served as carriers of known and potmitial urease inhibitors. These substances were physically attached to the absoibent core by exhaustion fiom their solutions and subsequent drying of the substrates. A few examples of materials treated this... 

Levy, R., M.A. Nichols, T.W. Miller Jr., Evaluation of superabsorbent polymer-pesticide formulations for prolonged insect control, in RR. Hall, P.D. Berger, and H.M. Collins (eds.). Pesticide Formulations and Application Systems, ASTM STP 1234, American Society for Testing and Materials, Philadelphia, PA, 1995, pp. 330-339. 

Professor Lechner has a PhD in chemistry from the University of Mainz, Germany. Since 1975 he is Professor of Physical Chemistry at the Institute of Chemistry of the University of Osnabriick, Germany. His scientific work concentrates on the physics and chemistry of polymers. In this area he is mainly working on the influence of high pressure on polymer systems, polymers for optical storage and waveguides as well as synthesis and properties of superabsorbers from renewable resources. 

Finally, with regard to revolutionary design, many systems adopt an acquisition layer or a combination of an acquisition layer and transport layers between the absorption core (Fig. 2) and the top sheet [9]. For the acquisition layer or the transport layer, either a crosslinked cellulose with a density of 0.04-0.1 g/cm, thermally fused PE/PP fibers, or a nonwoven cloth is used. The absorption core consists of surface-crosslinked superabsorbent polymer and pulp. In general, the concentration of the superabsorbent polymer is 40 to 60 wt %, and the weight of the polymer used per diaper is approximately 10 to 12 g [9,10]. 

A monodisperse hard sphere is packed in a faee-centered cube with the porosity of 0.295 and orthorhombic system with the porosity of 0.395. The porosities of dry superabsorbent polymers are generally 0.40 to 0.75, and are higher than a hard sphere, for example, a glass bead. However, the permeability of superabsorbent polymers is much lower than glass bends of a similar thiekness. 

The added mobility of the superabsorbent polymer chains in the final crosslinked system may be increased as the amount of solvent present during the crosslinking is increased (Figure 4). This variation Is most evident for polymers with fully-ionized swelling behavior. 

Using equation 6 a plot of the square of the particle radius versus the sorption time should be linear with a slope dependent on the swelling capacity and on the diffusion coefficient of the polymer/solvent system. In order to test this, a sample of DRYTECH superabsorbent polymer and a sample of Aridall 1078 from American Colloids were individually screened using U.S. Standard Sieves to obtain narrow particle size fractions. The sorption time data Is given in Table 1. The functional relation between the square of the radius and sorption time is shown in Figure 2. The result is consistent with a diffusion controlled absorption rate, and indicates that the simplifications of the diffusion equations are acceptable. Since the particle radius increases as the test proceeds, the initial value should be incremented by a factor equal to (22.8/Wp) -, which is the extent of swelling of the sample at time t, to the one-third power. 

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